1. Field
The present invention relates to a lithographic apparatus and a method for manufacturing a device.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate or part of a substrate. A lithographic apparatus can be used, for example, in the manufacture of flat panel displays, integrated circuits (ICs) and other devices involving fine structures. In a conventional apparatus, a patterning device, which can be referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of a flat panel display (or other device). This pattern can be transferred on (part of) the substrate (e.g., a glass plate), e.g., via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate.
Instead of a circuit pattern, the patterning means can be used to generate other patterns, for example a color filter pattern or a matrix of dots. Instead of a mask, the patterning device can comprise a patterning array that comprises an array of individually controllable elements. The pattern can be changed more quickly and for less cost in such a system compared to a mask-based system.
A flat panel display substrate is typically rectangular in shape. Lithographic apparatus designed to expose a substrate of this type can provide an exposure region that covers a full width of the rectangular substrate, or which covers a portion of the width (for example half of the width). The substrate can be scanned underneath the exposure region, while the mask or reticle is synchronously scanned through the projection beam. In this way, the pattern is transferred to the substrate. If the exposure region covers the full width of the substrate then exposure can be completed with a single scan. If the exposure region covers, for example, half of the width of the substrate, then the substrate can be moved transversely after the first scan, and a further scan is typically performed to expose the remainder of the substrate.
In a possible arrangement of a lithographic apparatus, an array of focusing elements, such as an array of lenses, is used to project a patterned beam of radiation onto the substrate. In such an arrangement, each focusing element projects a portion of the patterned beam of radiation onto the substrate. Accordingly, the radiation is projected onto the substrate as an array of sub-beams of radiation, forming spots on the substrate that are modulated according to the patterning device.
In order for a desired pattern to be successfully formed on the substrate, it is desirable for the spots projected on the substrate to be accurately positioned with respect to each other and to have a desired shape. The accuracy of the spot shapes and positions is primarily determined by the accuracy of manufacture of the array of focusing elements. It can be possible to compensate to some extent for some errors if these are precisely known. Accordingly, it can be desirable to determine the errors in the beam of radiation.
Therefore, what is needed is a system and method by which errors introduced in an array of spots by an array of focusing elements can be determined.